1. Field of the Invention
The present invention relates to a handover between heterogeneous networks, and more particularly, to a method of reconfiguring an IP address in handover between heterogeneous networks. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for enabling a mobile subscriber station to efficiently perform a handover between the heterogeneous networks.
2. Discussion of the Related Art
Generally, the object of IEEE802.21 in progress for International Standardization of inter-heterogeneous-network media independent handover is to enhance user's convenience for mobile subscriber station devices by providing seamless handover and service continuity between heterogeneous networks. An MIH function, an event trigger, a command service and an information service (IS) are defined as basic requirements.
A mobile subscriber station (MSS) is a multi-mode node that supports at least two interface types. Here, the interface can be, for instance, a wire-line type interface such as 802.3-based Ethernet, a wireless interface type based on IEEE802.XX such as IEEE802.11, IEEE802.15, IEEE802.16 and the like, an interface type defined by cellular standardization organization such as 3GPP and 3GPP2 and the like are possible.
FIG. 1 is a diagram of protocol stack architecture of a multi-mode mobile subscriber station.
Referring to FIG. 1, a multi-mode mobile subscriber station has a physical layer per mode and a medium access control layer per mode. And, an MIH layer lies below an IP layer.
Media independent handover (MIH) should be defined between IEEE802-series interfaces or between the 802-series interfaces such as the above-mentioned non-802-series interfaces defined by the cellular standardization organization such as 3GPP and 3GPP2. Moreover, a mobility supporting protocol of an upper layer such as Mobile IP and SIP (session initiation protocol) should be supported for the seamless handover service.
Mobile IPv4 is explained as follows.
A configuration of a network supporting a mobile IP includes a home agent, a foreign agent and a mobile subscriber station.
For the operation of the mobile IP, the following functions are required.
1) Agent Discovery
Agent discovery is a method of deciding whether a mobile subscriber station is currently connected to its home network or located at a foreign network. By this method, the mobile subscriber station can detect that it has been moved away into another network.
2) Registration
A function of registration offers a flexible mechanism enabling a service provided on a home network to be provided intact on a new network in a manner of delivering current position information to a home agent in case that a mobile subscriber station detects its migration into another network.
3) Routing
In case that a mobile subscriber station is linked to an external network, a function of routing is needed to properly route datagram to be transmitted from/to this mobile subscriber station.
4) Care of Address (CoA)
A mobile IP provides two kinds of methods of Foreign Agent (FA)-CoA and co-located CoA for establishment of care of address in case that a mobile node has moved away into another subnet.
FA-CoA is provided by a foreign agent via an agent advertisement message, in which an IP address of the foreign agent is used as a care of address. In the co-located CoA, a care of address is assigned to a mobile node via a Dynamic Host Configuration Protocol (DHCP) server located at a foreign network.
Mobile IPv6 is explained as follows.
Mobile IPv6 supports mobility more effectively than the mobile IPv4 and has extensibility better than that of the mobile IPv4. Basic elements and functions for the operation of the mobile IPv6 are explained as follows.
1) Mobile Node (MN): Host or router changing its network access.
2) Correspondent Node (CN): Host or router communicating with a mobile subscriber station.
3) Home Agent (HA): Router having registration information of a mobile subscriber station among routers in a home network to send datagram to a current position of the mobile subscriber station on an external network.
4) Care of Address (CoA): Internet Protocol (IP) address connected to a mobile subscriber station having moved away into an external network.
5) Binding: Matching CoA registered to a home agent by a mobile subscriber station and a home address of the corresponding mobile subscriber station together.
6) Binding Update (BU): Used by a mobile subscriber station to notify HA and CNs of its CoA.
7) Binding Acknowledge (BACK): Response message to BU.
8) Binding Request (BR): Message for requesting BU in case that a correspondent mobile subscriber station fails in receiving the BU before a timer of binding information of a mobile subscriber station expires.
9) CoA Acquisition: Position information can be automatically configured in mobile subscriber station shift using functions of neighbor discovery and address auto-configuration.
10) Router Optimization: Correspondent mobile subscriber station can directly communicate with a mobile node without a home agent after having stored binding information.
11) Address Auto-configuration
Auto-creation of an IP address is classified into a status preserving type address auto-configuration for acquiring an address using such a server as DHCP and a non-status address auto-configuration for creating an address of its own by a host side. In the method using the server, if a host side requests an address from a DHCP server, one of available addresses is allocated to the host side by the DHCP server. In the non-status type address auto-configuration, an address is created in a manner of binding its interface ID information and prefix information acquired from a router or well-known prefix information together.
FMIPv6 (Fast Handovers for Mobile IPv6) is explained as follows.
First of all, FMIPv6 is a protocol to reduce an overall handover delay in Layer 3 by making rapid progress of motion detection and NCoA (new care of address) acquisition based on handover estimation information in Layer 2. Basic elements and messages for the operation of FMIPv6 are explained in the following description.
1) PAR (previous access router): Default router prior to handover of a mobile node.
2) NAR (new access router): Default router estimated in a handover of a mobile node.
3) PCoA (previous care of address): Valid CoA of a mobile node in PAR subnet.
4) NCoA (new care of address): Valid CoA of a mobile node in NAR subnet.
5) RtSolPr (router solicitation for proxy): Making a request for information for potential handover via a message sent to PAR from a mobile node.
6) PrRtAdv (proxy router advertisement): offering information for a neighbor link via a message sent to a mobile node from PAR and operating as a trigger for a network initiated handover.
7) FBU (fast binding update): Message that a mobile node requests a PAR to change its traffic receiving place into NAR.
8) FBACK (fast binding acknowledge): Response message to FBU generated from PAR.
9) HI (handover initiation): Message sent to NAR from PAR to indicate a handover of a mobile node.
10) HACK (handover acknowledge): Message sent to PAR from NAR in response to HI.
11) FNA (fast neighbor advertisement): Message sent to NAR from a mobile node to indicate that the mobile node confirms a use of NCoA and accesses a new network in case of failing to receive FBACK yet.
MIH function is placed below an IP layer and facilitates a handover handling process using a trigger event and an input value from a second layer (Layer 2) such as information of other networks and the like. The MIH function can include input values based on user policy and configuration that can put influence on a handover process, and general interfaces are defined between the MIH function and a third layer (Layer 3) entity such as Mobile IP and SIP. These interfaces provide information about a first layer (Layer 1) (physical layer), the second layer (Layer 2) (MAC layer) and mobility management, and the MIH acquires information about lower layers and network with the help of the event and information service.
An upper management entity is placed in an upper layer to monitor and control statuses of various links within a mobile subscriber station and plays roles as a handover control function and a device manager function. In this case, the handover control function and the device manager function can be independently and respectively located. Alternatively, both of the functions may be included together as an upper management entity.
FIG. 2 is a diagram of functional entities and transport protocol of a mobile subscriber station and network having MIH functions, in which dotted lines indicate primitives, event triggers and the like.
For fast handover, a network layer needs to use information from a link layer to re-establish a connection as soon as possible. A link layer event helps to estimate a user's movement and may help a mobile subscriber station and network to prepare handover in advance.
A trigger for handover may start with a physical layer (PHY) and a medium access control layer (MAC). An origin of this trigger may be a local stack or a remote stack. FIG. 3 is a diagram of a trigger model.
An event trigger provides a state of a current signal, a state change of another network and an estimated change and also provides a change between a physical layer and a medium access control layer and attribute changes of a specific network.
Event types can be classified into PHY layer event, MAC layer event, Management event, L3 event, Application event and the like.
A basic trigger event is explained as follows.
First of all, ‘Link_Up’ occurs in case that a Layer 2 connection is established on a specific link interface and in case that L3 packets can be transferred from a higher layer. In this case, it is decided that all L2 configurations configuring the link are completed. And, event sources are ‘Local MAC’ and ‘Remote MAC’. Parameters of ‘Link_Up’ are shown in Table 1.
TABLE 1NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource from whichevent is generatedEventDestinationEVENT_LAYER_TYPEDestination to whichevent shall bedeliveredMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC address of oldaccess routerMacNewAccessRouterMAC AddressMAC address ofnew access routerNetworkIdentifierMedia SpecificNetwork Identifierusable in detectingchange of subnet
‘Link_Down’ occurs in case that an L2 connection is released on a specific interface and in case that it is unable to transfer L3 packets anymore. And, an event source is ‘Local MAC’. Parameters of ‘Link Down’ are shown in Table 2.
TABLE 2NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource from whichevent is generatedEventDestinationEVENT_LAYER_TYPEDestination to whichevent shall bedeliveredMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC address of oldaccess routerReasonCodeReason why link isreleased
‘Link_Going_Down’ occurs in case that it is estimated that an L2 connection is going to link down within a specific time. And, ‘Link Going Down’ may be a signal for initializing a handover procedure. Event sources are ‘Local MAC’ and ‘Remote MAC’. And, parameters of ‘Link_Going_Down’ are shown in Table 3.
TABLE 3NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource from whichevent isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich event shallbe deliveredMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC address ofold access routerMacNewAccessRouterMAC AddressMAC address ofnew access routerTimeIntervalTime in msecsEstimated timefor Link_DownConfidenceLevel%Estimated levelfor Link_Down oflink in aspecific timeUniqueEventIdentifierUsed in case thatEvent rollbackoccurs
‘Link_Going_Up’ occurs in case that it is estimated that an L2 connection is going to ‘link up’ within a specific time. And, ‘Link Going Up’ is used in case that it takes a long time for a network to be initialized. Event sources are ‘Local MAC’ and ‘Remote MAC’. And, parameters of ‘Link_Going_Up’ are shown in Table 4.
TABLE 4NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource from whichevent isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich event shallbe deliveredMacMobileTerminalMAC AddressMAC address ofMSSMacNewAccessRouterMAC AddressMAC address ofnew access routerTimeIntervalTime in msecsEstimated timefor Link_UpConfidenceLevel%Estimated level forLink_Up oflink in a specifictimeUniqueEventIdentifierUsed in case thatEvent rollbackoccurs
‘Link_Event_Rollback’ is combined with ‘Link_Going_Up’ or ‘Link_Going_Down’ to use. It is a trigger occurring in case that ‘Link_Going_Up’ or ‘Link_Going_Down’ is estimated not to occur within a specific time anymore despite that ‘Link_Going_Up’ or ‘Link_Going_Down’ is transmitted. Event sources are ‘Local MAC’ and ‘Remote MAC’. Table 5 shows parameters of ‘Link_Event_Rollback’.
TABLE 5NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource from whichevent isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich event shallbe deliveredMacMobileTerminalMAC AddressMAC address ofMSSMacNewAccessRouterMAC AddressMAC address ofnew access routerUniqueEventIdentifierUsed in case thatEvent rollbackoccurs
‘Link_Available’ indicates that a new specific link is usable or available. ‘Link_Available’ indicates possibility that a new base station or access point can provide a link quality better than that of a base station or access point currently accessed by a mobile subscriber station. Event sources are ‘Local MAC’ and ‘Remote MAC’. And, parameters of ‘Link_Available’ are shown in Table 6.
TABLE 6NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource from whichevent is generatedEventDestinationEVENT_LAYER_TYPEDestination to whichevent shall bedeliveredMacMobileTerminalMAC AddressMAC address ofMSSMacNewAccessRouterMAC AddressMAC address ofnew access routerMacOldAccessRouterMAC AddressMAC address of oldaccess router
‘Link_Parameters_Change’ is an event occurring in case that a variation of a link parameter value exceeds a specific limit. This can include a link layer parameter such as a link speed, QoS (quality of service), encryption value and the like. Event sources are ‘Local MAC’ and ‘Remote MAC’. And, parameters of ‘Link_Parameters_Change’ are shown in Table 7.
TABLE 7NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource fromwhich event isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich eventshall bedeliveredMacMobileTerminalMAC AddressMAC addressof MSSMacAccessRouterMAC AddressMAC addressof currentaccess routeroldValueOfLinkParameterOld value oflink parameternewValueOfLinkParameterNew value oflink parameter
‘MIH_Scan’ is a command used in discovering neighbor access points of a current access network by an upper layer. The ‘MIH_Scan’ is created if an upper layer entity requests a scan of an accessible network. If several links are requested, a plurality of Link_Scan commands can begin with various kinds of media san request informations.
MIH_Handover_Initiate.request is a primitive used by an upper layer entity to deliver an intention of a handover initiation between an MIH function of a mobile subscriber station and an MIH function of a network.
MIH_Handover_Initiate.response is a primitive which indicates corresponding information by selecting a preferable link according to situations of the requested links in response to MIH_Handover_Initiate.request.
MIH_Handover_Commit.request message is used to initiate buffering to be performed on data to be forwarded to a mobile subscriber station via the previous access point by informing a previous access point that a handover is substantially initiated for the selected link.
MIH_Handover_Commit.response message is a response message to the MIH_Handover_Commit.request message used to indicate a success or failure of handover.
FIG. 4 is an exemplary diagram of a trigger occurring until a new link is created since a quality of link currently accessed by a mobile subscriber station is degraded.
Information Service provides detailed information for a network necessary for network discovery and selection and should be accessible by any kind of network. The information service should include information elements such as link access parameter, security mechanism, neighbor map, location, service provider and other access information, cost of link and the like.
A detailed operational procedure of Mobile IPv4 is explained as follows.
First of all, the basic object of Mobile IPv4 is to support transparent mobility of an upper layer and needs additional functions of mobile host, home agent and foreign agent. Yet, in case of not using path optimization, a change of a correspondent node communicating with a mobile subscriber station is unnecessary. In this case, the mobile host represents an IP host supported by mobility. The home agent is a router that sustains location information for the mobile host and performs tunneling. And, the foreign agent means a router supporting mobility in a foreign network.
Basic actions in Mobile IPv4 can be explained as shown in FIG. 5.
An action per step in FIG. 5 is explained as follows.
(1) In case that a mobile host moves away into a foreign network from its home network, the mobile host recognizes that it has moved by receiving an advertisement message broadcast from the foreign network and then registers a temporary address (CoA) indicating its current location to a home agent in the home network.
(2) In this case, CoA is an IP address (FA-CoA) of a foreign agent or an address allocated to the mobile host via DHCP or the like by the foreign network. Packets sent to the mobile host from outside are transferred to the home network and these packets are picked up by a home agent recognizing a movement of a mobile subscriber station.
(3) The home agent encapsulates a packet delivered to the mobile host by targeting an address of FA as a destination and then delivers it to the foreign agent.
(4) The delivered encapsulated packet is recovered into an initial delivery packet by being de-capsulated by the foreign agent and is then delivered to the mobile host finally.
(5) The packet to be delivered to a correspondent host from the mobile host can be directly delivered via the foreign agent or can be delivered using a reverse tunnel in case of a problem of ingress filtering.
Major functions necessary for Mobile IP are explained as follows.
1) Agent Discovery
Agent discovery is a method of deciding whether a mobile subscriber station is currently connected to its home network or located at a foreign network. By this method, the mobile subscriber station can detect that it has been moved away into another network.
Mobile IP extends conventional ICMP (Internet control message protocol) router discovery [IETF RFC 1256]. An agent advertisement message periodically broadcast by an agent (home agent, foreign agent) makes a mobility agent advertisement extension included in an ICMP router advertisement message to be transmitted. ‘Agent Solicitation’ message transmitted by a mobile subscriber station to find an agent uses the same method of a conventional ‘ICMP router Solicitation’ message.
2) Registration
A function of registration offers a flexible mechanism enabling a service provided on a home network to be provided intact on a new network in a manner of delivering current position information to a home agent in case that a mobile subscriber station detects its migration into another network. Mobile IP defines two different registration procedures. In case of using FA-CoA, a mobile subscriber station should make a registration via a foreign agent. In case of using co-located CoA, a mobile subscriber station makes a direct registration to a home agent.
3) Routing
In case that a mobile subscriber station is linked to an external network, a function of routing is needed to properly route datagram to be transmitted from/to this mobile subscriber station. The datagram includes multicast and broadcast packets as well as unicast packets.
FIG. 6 is a diagram for explaining a basic operation of Mobile IPv6 according to a related art.
First of all, operational steps of Mobile IPv6 can be sequentially explained in FIG. 6.
0. MN moves away into Subnet B from Subnet A
1. MN detects a migration using prefix information of RA message and NUD (neighbor unreachable detection) mechanism.
2. Obtaining CoA by itself through ‘Address auto-configuration’
3. Sending BU message to inform HA of the obtained CoA
4. HA binds a home address of MN and CoA together and then sends BAck in response to BU.
5. CN firstly communicating with MN transmits a packet by setting a destination address to the home address of MN because of failing in detecting the migration of MN.
6. HA managing MN intercepts the packet to tunnel it to a current position of MN.
7. MN having received the tunneled packet decides that the CH does not have binding information and then notifies CN of its CoA by sending BU message to the CN.
8. After having stored the binding information, CN directly communicates with MN using the information.
FIG. 7 and FIG. 8 are diagrams for explaining an operational process of FMIPv6. FIG. 7 shows an operational procedure in ‘proactive’ mode and FIG. 8 shows an operational procedure in ‘reactive’ mode. There are a ‘proactive’ mode for sending FBU/FBACK message from/to a link of PAR and a ‘reactive’ mode for sending FBU/FBACK message from/to a link of NAR. In case of ‘proactive’ mode, certainty of a created NCoA is examined prior to releasing a connection to PAR. In case of ‘reactive’ mode, certainty of NCoA is checked after a mobile node has arrived at a new subnet.
An operational procedure of ‘proactive mode’ is explained with reference to FIG. 7 as follows.
1) A mobile node discovers APs available for handover based on L2 layer information (e.g., scan in a wireless LAN system) and then sends RtSolPr message to PAR to obtain subnet information corresponding to the discovered AP identifiers.
2) The PAR having received the RtSolPr message puts the subnet information corresponding to the APs in a tuple in [AP-ID, AR-Info] format and then sends a PrRtAdv message to the mobile node. This message can be occasionally sent ‘solicit’ after the mobile node has performed router detection.
3) The mobile node creates a new care of address (NCoA) based on AR-Info within the PrRtAdv message.
4) The mobile node sends FB message that requests the PAR to bind PCoA and NCoA together so that packets arriving at the PAR can be tunneled to NAR.
5) The PAR sends a notification message indicating that the mobile node will hand over to the NAR, i.e., HI. The NAR having received the HI message performs an overlapping check of the NCoA created by the mobile node. If the NCoA is not suitable as a result of the overlapping check, the NAR newly configures a CoA for the mobile node.
6) The NAR sends HACK as a response message for the HI to the PAR. In this case, a newly created NCoA can be included.
7) The PAR having received the HACK sends FBACK to the mobile node and the NAR and informs that the PAR will initiate to tunnel a packet of the mobile node to an address of a real NCoA. In this case, a connection between the mobile node and the PAR is released.
8) The packet having arrived at the PAR is forwarded to the NAR.
9) The mobile node sends FNA message to the NAR as soon as a new link to the NAR is established. So, it is informed that the mobile node itself is connected to a network of the NAR.
10) The packet is transmitted via the NAR.
And, an operational procedure of ‘reactive mode’ is explained with reference to FIG. 8 as follows.
1) A mobile node discovers APs available for handover based on L2 layer information (e.g., scan in a wireless LAN system) and then sends RtSolPr message to PAR to obtain subnet information corresponding to the discovered AP identifiers.
2) The PAR having received the RtSolPr message puts the subnet information corresponding to the APs in a tuple in [AP-ID, AR-Info] format and then sends a PrRtAdv message to the mobile node. This message can be occasionally sent ‘solicit’ after the mobile node has performed router detection.
3) The mobile node creates a new care of address (NCoA) based on AR-Info within the PrRtAdv message.
4) The mobile node initiates a procedure of forwarding an arriving packet to the NAR immediately in a manner of encapsulating FBU message in FNA message as soon as connected to the NAR. And, the mobile node makes the NAR check whether the NCoA is valid.
5) The NAR sends FB message to the PAR to bind PCoA and NCoA together. If the NCoA is not valid in the FBU received by the NAR, the NAR discards FBU packet and sends a router advertisement having a substitute address therein.
6) The PAR sends FBACK as a response message for the FBU to the NAR. In this case, a tunneling establishment is completed between an actual PAR and NAR.
7) The packet having arrived at the PAR is forwarded to the NAR.
8) The packet is transmitted via the NAR.
However, as mentioned in the above description, the related art has the following problems.
First of all, the L2 handover procedure and the L3 handover procedure are independently generated in case of using MIPv4, MIPv6 or FMIPv6. Namely, the L3 handover is carried out after the L2 handover has been completed. So, a corresponding delay takes place.
Secondly, if a network knowing the L2 handover directly sends a message for the L3 handover, the L3 does not know this. So, an unnecessary message transmission is needed.
Thirdly, in case that communications between media independent handover entities are available for a field to which the present invention is applied, no change may be made to use in IP address re-configuration when a handover is carried out between homogeneous networks.